Sludge Watch ==> Growing Crops for Biofuels Take a Toll on Soil Health

[Maureen Reilly]

http://www.agcanada.com/custompages/stories_story.aspx?mid=192&id=1301

Cheap biofuel feedstocks take a toll on soil health 	07.09.2007
Biofuel experts are already looking beyond grains for cheaper feedstocks 
such as straw or corn stover. But there is a price to be paid when you 
remove biomass that normally goes back to the soil

By Tom Button


It can take as little as 3 years to effectively burn your way through most 
of the 50 to 100 tonnes of humified organic matter in a typical acre of 
Ontario's corn producing soil. Once you burn through that organic matter, 
however, it may realistically take 3 lifetimes to build it back up.

That imbalance has Canadian soil specialists shaking their heads in 
disbelief at some of the bio-energy concepts that are being touted as 
representing the brave new world of renewable energy.

"If it burns up your organic matter, there's nothing renewable about it," 
snaps a worried Keith Reid, soil and fertility specialist for the Ontario 
Ministry of Agriculture, Food and Rural Affairs (OMAFRA).

Those concepts, based on removing whole-plant top growth from the field and 
not putting any organic residues back, have the potential to zap the 
productivity out of today's soils almost as quickly as turning off a light 
switch. But they aren't the only plans that have soils scientists on the 
alert. Even ethanol and biodiesel proposals that rely on corn and soybeans 
will prove damaging to Ontario's long-term agricultural productivity if high 
prices lure more acres into monoculture and away from sound rotations, the 
scientists warn.

"There's no free lunch," says Ed Gregorich, soil scientist for Agriculture 
and Agri-Food Canada at Ottawa. "Organic matter is the key to soil 
productivity. If we allow it to be depleted, there might be a short-term 
financial gain but we'll be faced with compaction, poor soil structure and a 
whole suite of other long-term soil quality issues."

In fact, it turns out that in order to maintain any hope of sustainability, 
most soils have very little cushion. Now, a team of OMAFRA extension 
specialists including Kevin McKague, Adam Hayes and Christine Brown, has 
taken a first provisional stab at calculating how much cushion exists.

The OMAFRA team based their calculations on existing research showing it 
takes 3 tonnes of carbon per year to simply maintain the organic matter 
content of a hectare of moldboard-plowed corn soil. (Carbon is the building 
block of organic matter.) Less carbon is needed in no-till soils, in part 
because of lower erosion rates, but also because the mere turning over of 
plowed soils exposes more organic matter to atmospheric oxygen, where it 
undergoes chemical processes similar to combustion. Even so, a no-till field 
still needs a carbon injection of about 2.1 tonnes per hectare per year.

The OMAFRA team calculates that Ontario could only afford to divert 2.7% of 
its corn stover to off-farm processing, assuming that the spent stover isn't 
returned to the field after processing. Even in years with growthy crops, 
such as 2005, the province could only export 9.5% of its stover.

With no-till, the stover available for harvest is higher, but if growers 
hope to be sustainable in the long-term, they'd be limited to selling a 
quarter of their corn residue, the team says.

For other crops, the outlook is even more restricted. Not surprisingly, 
there's essentially no room to export soybean top growth, since soybeans 
produce so little organic material. More surprising, though, is the team's 
conclusion that Ontario also cannot afford to export wheat straw off-farm 
for energy processing. That's because 450,000 tonnes are already taken off 
for straw, and that's already stretching the limits.

"We need to look at the soil as a finite resource," McKague says. "We 
haven't got a lot of organic matter to spare."

Indeed, soil specialists generally applaud Ontario's grain farmers just for 
being able to hold onto current organic matter levels, following rapid 
declines in the '70s and '80s when many farms gave up their livestock and 
therefore had no manure source, and when they also aggressively moldboard 
plowed.

Progress has stalled, however. McKague points out that while about half of 
Ontario's cashcrop soils are managed with conservation tillage, less than 
20% of cornfields are no-tilled, and that number hasn't been growing.

"We won't be doing any favors for anyone, least of all ourselves, if we 
damage that equilibrium just to grow energy crops," McKague says. "None of 
us are against using farms to grow energy. That's not what we're saying. But 
we do need to get it right, using minimum tillage as much as possible and 
not taking off more bio-materials than the soil can sustain."

Like McKague, Reid thinks farmers need to draw the line for themselves. 
"We're already seeing signs that some of these promoters are either 
underestimating or they're completely ignoring the impact their plans are 
going to have on organic matter," Reid says. "Fortunately, the farmers are 
asking tough questions, and they're going to have to keep on asking those 
questions."

Indeed, Gregorich says the best outcome for everyone, including farmers as 
well as consumers may be to actually increase the amount of organic matter 
in our soils. That would have the double advantage, Gregorich explains, of 
boosting soil productivity and also lowering the level of climate-warming 
carbon dioxide in the atmosphere.

Fortunately, Gregorich adds, scientists in the past decade have vastly 
improved their ability to provide advice about organic matter. Detailed 
studies are unraveling the complex nature of organic matter, delving into 
the roles of each of its myriad components instead of treating organic 
matter, as in past, as a single uniform substance.

"Organic matter is going to be a critical issue, one of the critical 
issues," McKague says. "Society is saying it needs us to help diversify our 
energy future, but we also need to look after the future of our soils."  CG